Multipath equalization for MIMO multiuser systems

ABSTRACT

Interference rejection ( 85 ) can be applied to a wireless communication signal with reduced computational complexity by producing from a sample vector (y) a plurality of vectors (w) that are smaller than the sample vector. The interference rejection operation can then be applied to each of the smaller vectors individually to decide communication symbols represented by the sample vector.

[0001] This application claims the priority under 35 U.S.C. 119(e)(1) ofcopending U.S. provisional application No. 60/298,785, filed on Jun. 15,2001, and incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The inventions relates generally to wireless communications and,more particularly, to wireless CDMA communications.

BACKGROUND OF THE INVENTION

[0003] Copending U.S. Ser. No. 10/107,275 (docket TI-32842) filed onMar. 26, 2002 discloses subject matter related to that disclosed herein,and is incorporated herein by reference. Symbols C_(k), s_(k), Ψ and r,as used in incorporated U.S. Ser. No. 10/107,275, correspondrespectively to S_(k), b_(k), H and y as used herein.

[0004]FIG. 1 diagrammatically illustrates an example of a conventionalCDMA transmitter apparatus. As shown in FIG. 1, the communication datais first applied to a channel encoding section 11 whose output is thenfed to a channel interleaver 12. The output of the channel interleaver12 is input to a modulator 13, for example a QPSK modulator or an M-QAMmodulator. The modulator 13 outputs communication symbols to a MIMO/ST(multiple input-multiple output/space-time) coding section 14. Theoutput of the MIMO/ST coding section 14 is input to a multi-antennaspreading section 15 which drives a plurality of transmit antennas.Examples of space-time (ST) coding at 14 include STTD, double STTD andOTD coding.

[0005]FIG. 2 illustrates examples of the MIMO/ST coding section 14 andspreading section 15 of FIG. 1 in more detail. As show in FIG. 2, theMIMO/ST coding section 14 includes a plurality of MIMO transformerswhich perform MIMO transforms on communication symbols received from themodulator 13. Each MIMO transformer receives symbols associated with oneof K specific sources. The K sources can be associated with K differentusers, or can be associated with a single user, or one or more groups ofthe sources can be associated with one or more respective users whilethe rest of the sources are individually associated with other users.Assuming P transmit antennas, each MIMO transformer produces P outputs,and all KP outputs are applied to the multi-antenna spreading section15. For each of the P outputs provided by one of the K MIMOtransformers, the multi-antenna spreading section 15 applies one of Kspreading codes to those P outputs. The signals that result fromapplication of the spreading codes are then combined by P combiners asshown for transmission on the P transmit antennas.

[0006]FIG. 3 diagrammatically illustrates an exemplary portion of aconventional CDMA receiver which can receive the signals transmitted bythe conventional transmitter of FIGS. 1 and 2. As shown in FIG. 3,signals received by a plurality of antennas are sampled at the chip rate(sampling could also be done above the chip rate). With N_(C) chips persymbol, and a symbol detection window size of N symbols, the samplingsection 32 of FIG. 3 collects a total of N_(C)×N chips per detectionwindow, as illustrated at 31 and 33 in FIG. 3. The received signal y ofFIG. 3 can be expressed as follows: $\begin{matrix}{\underset{\_}{y} = {{\sum\limits_{k = 1}^{K}{\sqrt{\rho_{k}}H_{k}S_{k}{\underset{\_}{b}}_{k}}} + \underset{\_}{n}}} & (1)\end{matrix}$

[0007] or, in matrix form: $\begin{matrix}{\underset{\_}{y} = \begin{bmatrix}{y_{1}(0)} \\{y_{2}(0)} \\\vdots \\{y_{Q}(0)} \\\vdots \\{y_{1}\left( {{N_{c}N} - 1} \right)} \\{y_{2}\left( {{N_{c}N} - 1} \right)} \\\vdots \\{y_{Q}\left( {{N_{c}N} - 1} \right)}\end{bmatrix}} & (2)\end{matrix}$

[0008] where Q is the number of receive antennas, and Q>P. In equation 1above, the matrix H_(k) represents the transmission channel associatedwith the kth source (which is known, e.g., from conventional channelestimation procedures), ρ_(k) is the power of the kth source, S_(k) isthe spreading code matrix for the kth source, b_(k) is the data symbolvector for the kth source and n is white noise. The dimension of thereceived signal vector y is N_(c)NQx1, the channel matrix H_(k) is aN_(c)NQxN_(c)NP matrix, the spreading code matrix S_(k) is a N_(c)NPxNPmatrix, and the vector b_(k) has a dimension of NPx1.

[0009] The data symbol vector b_(k) can be written in matrix form asfollows: $\begin{matrix}{{\underset{\_}{b}}_{k} = \begin{bmatrix}{b_{k,1}(0)} \\{b_{k,2}(0)} \\\vdots \\{b_{k - P}(0)} \\\vdots \\{b_{k,1}\left( {N - 1} \right)} \\{b_{k,2}\left( {N - 1} \right)} \\\vdots \\{b_{k,P}\left( {N - 1} \right)}\end{bmatrix}} & (3)\end{matrix}$

[0010] where k is the index in equation 1 for the K sources of FIG. 1, Pis the number of transmit antennas, and 0 to N−1 represent the N symbolsin the symbol detection window. Rewriting a portion of equation 1 asfollows:

{square root}{square root over (ρ_(k))}H _(k) S _(k) =A _(k)  (4)

[0011] then equation 1 can be further rewritten as follows:$\begin{matrix}{\underset{\_}{y} = \left\lbrack \begin{matrix}A_{1} & \cdots & {{\left. A_{K} \right\rbrack \begin{bmatrix}{\underset{\_}{b}}_{1} \\\vdots \\{\underset{\_}{b}}_{K}\end{bmatrix}} + \underset{\_}{n}}\end{matrix} \right.} & (5)\end{matrix}$

[0012] Equation 5 above can in turn be rewritten in even moregeneralized format as follows:

y=ab+n  (6)

[0013] The goal is to solve for the vector b. One way to do so isconventional multi-user detection with the linear zero forcing (LZF)solution (see also FIG. 4) given by:

z=F _(MZ) y=(a ^(H) a)⁻¹ a ^(H) y=b+(a ^(H) a)⁻¹ a ^(H) n  (7)

[0014] wherein z has a vector format as follows: $\begin{matrix}{\underset{\_}{z} = \begin{bmatrix}{\underset{\_}{z}}_{1} \\\vdots \\{\underset{\_}{z}}_{K}\end{bmatrix}} & (8)\end{matrix}$

[0015] and wherein the components of z have the following format$\begin{matrix}{{\underset{\_}{z}}_{k} = \begin{bmatrix}{z_{k,1}(0)} \\{z_{k,2}(0)} \\\vdots \\{z_{k,P}(0)} \\\vdots \\{z_{k,1}\left( {N - 1} \right)} \\{Z_{k,2}\left( {N - 1} \right)} \\\vdots \\{Z_{k,P}\left( {N - 1} \right)}\end{bmatrix}} & (9)\end{matrix}$

[0016] and wherein ${\begin{bmatrix}{z_{k,1}(0)} \\{z_{k,2}(0)} \\\vdots \\{z_{k,P}(0)}\end{bmatrix} \equiv {{\underset{\_}{z}}_{k}(0)}},{\begin{bmatrix}{z_{k,1}(1)} \\{z_{k,2}(1)} \\\vdots \\{z_{k,P}(1)}\end{bmatrix} \equiv {{\underset{\_}{z}}_{k}(1)}},{{etc}.},$

[0017] so equation 9 can also be written as $\begin{matrix}{{\underset{\_}{z}}_{k} = \begin{bmatrix}{{\underset{\_}{z}}_{k}(0)} \\{{\underset{\_}{z}}_{k}(1)} \\\vdots \\{{\underset{\_}{z}}_{k}\left( {N - 1} \right)}\end{bmatrix}} & (10)\end{matrix}$

[0018] Multiplying through equation 6 by a^(H) gives:

a ^(H) y=a ^(H) ab+a ^(H) n  (11)

[0019] The superscript “H” herein designates the conjugate and transposeoperation. Neglecting the noise in equation 11 gives:

a ^(H) y=a ^(H) ab  (12)

[0020] Therefore, an estimate, {circumflex over (b)} of the vector b isgiven by: $\begin{matrix}{\underset{\_}{\hat{b}} = {{\left( {a^{H}a} \right)^{- 1}a^{H}\underset{\_}{y}} = \begin{bmatrix}{\underset{\_}{\hat{b}}}_{1} \\\vdots \\{\underset{\_}{\hat{b}}}_{K}\end{bmatrix}}} & (13)\end{matrix}$

[0021] This estimate {circumflex over (b)} represents the solution as:

{circumflex over (b)}=z; {circumflex over (b)}=z _(k); and {circumflexover (b)} _(k)(n)=z _(k)(n)  (14)

[0022] for k=1, . . . K and n=0, . . . N−1

[0023] For downlink scenarios, the channels experienced by all thesources from the base station to a mobile unit are common. That is,H_(k)=H for k=1, . . . , K. In this case, chip equalization techniquescan be used.

[0024] For conventional chip equalization approaches, the followingvector can be defined: $\begin{matrix}{\underset{\_}{x} = {\sum\limits_{k = 1}^{K}{\sqrt{\rho_{k}}S_{k}{\underset{\_}{b}}_{k}}}} & (15)\end{matrix}$

[0025] and, substituting into equation 1:

y=Hx+n  (16)

[0026] Conventional chip equalization techniques can be used to equalizefor the channel H in equation 16. Applying the linear zero forcingtechnique to equation 16 yields

F _(cZ) y=(H ^(H) H)⁻¹ H ^(H) y=x+noise  (17)

[0027] The zero-forcing, chip equalization operation of equation 17above produces the output 51 in the FIG. 5 example of a conventionalchip equalizer with linear zero forcing. From the output 51 in FIG. 5,the components of the vector z shown above in equation 8 can be producedby applying the appropriate despreading matrices to the output 51. Thus,for k equal 1, 2, . . . K,

z _(k) =S _(k) ^(H) x+noise  (18)

[0028] Using chip equalization and linear zero forcing, the componentsof the vector z are given by

z _(k)={square root}{square root over (ρ_(k))}b _(k) +noise  (19)

[0029] Although zero-forcing criterion completely eliminates theinterference among different sources, it results in excessive noiseenhancement. A better criterion is minimum mean squared error (MMSE)since it optimally trades off noise enhancement and residualinterference.

[0030]FIG. 6 diagrammatically illustrates an exemplary conventionalmulti-user detection arrangement utilizing the linear minimum meansquared error (LMMSE) solution. The background for the technique of FIG.6 is demonstrated by the following equations 20-24. The expected valuesfor the vectors b and n above are given by:

E[bb ^(H) ]=εI  (20)

E[nn ^(H)]=σ² I  (21)

[0031] The LMMSE solution for multi-user detection is the functionF_(MM) which minimizes the expression:

_(F) _(MM) ^(min) E∥F _(MM) y−b∥ ²  (22)

[0032] The desired function F_(MM) is $\begin{matrix}{F_{MM} = {\left( {{a^{H}a} + {\frac{\sigma^{2}}{ɛ}I}} \right)^{- 1}a^{H}}} & (23)\end{matrix}$

[0033] and this function F_(MM) can be applied to the received signal toobtain the desired vector z as follows:

z=F _(MM) y  (24)

[0034] The LMMSE solution for chip equalization is given by:$\begin{matrix}{F_{CM} = {\left( {{H^{H}H} + {\frac{\sigma^{2}}{ɛ}I}} \right)^{- 1}H^{H}}} & (25)\end{matrix}$

[0035] Applying the function F_(CM) to the received signal, asillustrated in the conventional LMMSE chip equalizer example of FIG. 7,gives:

F _(CM) y=F _(CM) Hx+F _(CM) n  (26)

[0036] It is known in the art to apply iterative (i.e., successive ordecision feedback) interference cancellation techniques in conjunctionwith multi-user detection or chip equalization. Iterative techniquesprovide improved interference cancellation, but requiredisadvantageously complex computations when applied to large matricessuch as F_(CZ), and F_(CM), F_(MZ) and F_(MM) above. This is because ofthe large number (NKP) of iterations required.

[0037] It is therefore desirable to provide for iterative interferencecancellation while avoiding complex matrix computations such asdescribed above. The present invention advantageously isolates blocks ofa conventional chip equalizer output, and applies interference rejectiontechniques to the isolated blocks to improve the symbol estimation atthe receiver. The present invention also advantageously isolates blocksof a conventional multi-user detector output, and applies interferencerejection techniques to the isolated blocks to improve the symbolestimation at the receiver. The block isolation advantageously reducesthe complexity of the matrix calculations in the interference rejection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 diagrammatically illustrates a conventional example of awireless CDMA transmitter.

[0039]FIG. 2 illustrates a portion of the transmitter of FIG. 1 in moredetail.

[0040]FIG. 3 diagrammatically illustrates a portion of a conventionalreceiver for receiving symbols transmitted by the transmitter of FIGS. 1and 2.

[0041]FIG. 4 diagrammatically illustrates conventional multi-userdetection with the LZF solution.

[0042]FIG. 5 diagrammatically illustrates conventional chip equalizationwith the LZF solution.

[0043]FIG. 6 diagrammatically illustrates conventional multi-userdetection with the LMMSE solution.

[0044]FIG. 7 diagrammatically illustrates conventional chip equalizationwith the LMMSE solution.

[0045]FIG. 8 diagrammatically illustrates pertinent portions ofexemplary embodiments of a wireless CDMA receiver including chipequalization, block isolation and successive interference cancellationaccording to the invention.

[0046]FIG. 9 diagrammatically illustrates exemplary isolation operationswhich can be performed by the receiver of FIG. 8.

[0047]FIG. 10 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a wireless CDMA receiver including chipequalization, block isolation and successive interference cancellationaccording to the invention.

[0048]FIG. 11 illustrates exemplary isolation operations which can beperformed by the receiver of FIG. 10.

[0049]FIG. 12 diagrammatically illustrates pertinent portions ofexemplary embodiments of a wireless CDMA receiver including chipequalization, block isolation, spatial channel reintroduction andsuccessive interference cancellation according to the invention.

[0050]FIG. 13 diagrammatically illustrates pertinent portions ofexemplary embodiments of a wireless CDMA receiver including multi-userdetection, block isolation and successive interference cancellationaccording to the invention.

[0051]FIG. 14 illustrates exemplary isolation operations which can beperformed by the receiver of FIG. 13.

[0052]FIG. 15 diagrammatically illustrates pertinent portions ofexemplary embodiments of a wireless CDMA receiver including multi-userdetection, block isolation, spatial channel reintroduction andsuccessive interference cancellation according to the invention.

[0053]FIG. 16 illustrates exemplary isolation operations which can beperformed by the receiver of FIG. 15.

[0054]FIG. 17 diagrammatically illustrates pertinent portions ofexemplary embodiments of the successive interference cancellationapparatus of FIGS. 8, 10, 12, 13 and 15.

[0055]FIG. 18 illustrates in tabular format inputs and outputs of thecontroller of FIG. 17 according to various exemplary embodiments of theinvention.

[0056]FIG. 19 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a wireless CDMA receiver including blockisolation and maximum likelihood detection according to the invention.

[0057]FIG. 20 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a wireless CDMA receiver according to theinvention.

DETAILED DESCRIPTION

[0058] In exemplary embodiments of a receiver input processing sectionaccording to the invention, chip equalization or multi-user detection isapplied to the aforementioned vector y (see also FIG. 3), and theresulting vector is then processed appropriately to produce a pluralityof much smaller vectors. Successive interference cancellation techniquescan then be applied individually to each of the smaller vectors producedby the receiver input processing section, thereby reducing thecomputational complexity of the successive interference cancellationoperation. In some embodiments, each of the smaller vectors correspondsto the P symbols of a given source that are transmitted on P transmitantennas (see also FIG. 2) during a given symbol interval.

[0059] In some exemplary chip equalization embodiments of the invention(illustrated by FIG. 8) the operation F_(C)H (where F_(C=)F_(CZ) orF_(CM)) can be expressed as follows: $\begin{matrix}{{F_{C}H} = {\underset{\underset{B}{}}{\begin{bmatrix}B_{o} & \quad & \quad & \quad \\\quad & B_{1} & \quad & \quad \\\quad & \quad & ⋰ & \quad \\\quad & \quad & \quad & B_{N - 1}\end{bmatrix}} + \left( {{F_{C}H} - \begin{bmatrix}B_{o} & \quad & \quad & \quad \\\quad & B_{1} & \quad & \quad \\\quad & \quad & ⋰ & \quad \\\quad & \quad & \quad & B_{N - 1}\end{bmatrix}} \right)}} & (27)\end{matrix}$

[0060] where B_(i) is the i-th block on the diagonal of F_(C)H. This ischosen so that the residual interference and the signal have zerocorrelation for that particular block i. However, in general, otherchoices for B are possible with appropriate filtering afterwards. Thesize of each B_(i) is N_(c)P×P.

[0061] Combining equations (26) and (27) yields

F _(C) y=Bx+(F _(C) H−B)x+F _(C) n  (28)

Let {tilde over (n)}=(F _(C) H−B)x+F _(C) n  (28A)

[0062] Isolating N blocks of B (which is block diagonal) results in

[F _(C) y] _(i) =B _(i) x _(i) +ñ _(i) , i=0, . . . , N−1,  (29)

[0063] where each [F_(C)y]_(i) is an N_(c)P×1 component of the N_(c)PN×1vector F_(C)y produced by chip equalizer 81 (also referred to herein asa linear front end detector). This isolation operation is performed at82 in FIG. 8, and is illustrated in FIG. 9. The vector x_(i) of equation(29) is a P×1 vector, and block B_(i) is an N_(c)P×P matrix.

[0064] Now, E[ñ_(i)ñ_(i) ^(H)]=C_(i) is readily calculated fromequations (28) and (28A). Because x and n are uncorrelated,E[ññ^(H)]=(F_(C)H−B)(F_(C)H−B)^(H)+F_(C)F_(C) ^(H), and C_(i) is simplya (N_(C)P×N_(C)P) block on the diagonal of E[ññ^(H)]. E[{tilde over(x)}_(i)ñ^(H)]=0, because the blocks on the diagonal of (F_(c)H−B) are0, and E[{tilde over (x)}_(i){tilde over (x)}_(i) ^(H)]=ε.

[0065] Now, at 83 in FIG. 8, a despreader despreads the N isolatedblocks for every source k. For k=1, . . . K, the despreader 83multiplies each [F_(C)y]_(i) by a timewise corresponding P×N_(c)Pportion, D_(k)(i), of the NP×N_(C)NP matrix S_(k) ^(H). Withdespreading, the signal model of equation (29) yields a P×P matrixchannel (D_(k)(i)B_(i)) for every space symbol of each of the K sources,resulting in KN vectors of dimension P×1 (one vector for each sourceduring each symbol time), together with associated noise {circumflexover (n)} whose correlation is calculated as D_(k)(i)C_(i)D_(k)(i)^(H).These KN vectors are output by despreader 83.

[0066] Successive spatial interference cancellation (zero forcing orMMSE), as described in more detail below, can then be applied to the KNvectors to produce the symbol decisions. This is done by an interferencecancellation apparatus 85.

[0067] In other exemplary chip equalization embodiments shown in FIG.10, the despreading is done at 102 before the block isolation. In suchembodiments, the full matrix S_(k) ^(H) (for k=1, . . . K) of dimensionNP×N_(c)NP is applied to the N_(c)NP×1 vector F_(C)y at 102 to produceF_(C)′y, which includes K vectors of dimension NP×1. These K vectors(one for each source) are then separated (isolated) at 103 into KNvectors of dimension P×1, as shown in FIG. 11.

[0068] Applying the signal model of equations (27)-(29) to the FIG. 10embodiments, F_(C) is replaced by F_(c)′=S_(k) ^(H)F_(c). F_(c)H is anN_(c)NP×NP matrix, so F_(c)′H=S_(k) ^(H)F_(c)H is an NP×NP matrix whoseN diagonal blocks are P×P matrices. These N diagonal blocks areanalogous to {circumflex over (B_(i))} above, and are designated{circumflex over (B_(i))}. The blocks {circumflex over (B_(i))} can beused to form a matrix {circumflex over (B)} analogous to matrix B above.Also, C_(i) can be calculated for the FIG. 10 embodiments analogously tothe calculation of C_(i) for the FIG. 8 embodiments, but with F_(c) andB replaced by F_(c)′ and {circumflex over (B)}, respectively.

[0069] Other exemplary chip equalization embodiments (shown in FIG. 12)first despread at 121 by {tilde over (S)}_(k)=I_(PN)

s_(k), where s_(k) is the spreading sequence of the k-th source and

is the Kronecker product:

{tilde over (S)} _(k) =F _(C) y={tilde over (S)} _(k) F _(C) Hx+{tildeover (S)} _(k) F _(C) n, where F _(C) =F _(CZ) or F_(CM),

[0070] =b_(k)+{circumflex over (n)} (an NP×1 vector where n is residualinterference).

[0071] Now, at 122, a separator “isolates” one space-symbol at a timefor i=1, . . . ,N and k=1, . . . K One space-symbol corresponds to Psymbols of a given source on P transmit antennas during a given symboltime. This isolation operation (the same as performed by separator 103)yields KN vectors of dimension P×1,

M _(k)(i)=b _(k)(i)+{circumflex over (n)}(i) (for k=1, . . . K and i=1,. . . N)

[0072] Now, at 123, precondition (i.e. reintroduce the spatial channel)to whiten the residual interference n (i):

G _(C)(i)M _(k)(i)=G _(C)(i)b _(k)(i)+G _(C)(i){circumflex over (n)}(i),

[0073] where G_(C)(i)=(E[{circumflex over (n)}(i){circumflex over(n)}(i)^(H)])^(−1/2)

[0074] This G_(C)(i) is introduced to whiten the residual interference,but any other G_(C)(i) is possible with appropriate filteringafterwards.

[0075] For MMSE chip equalization,${{E\left\lbrack {\hat{\underset{\_}{n}}{\hat{\underset{\_}{n}}}^{H}} \right\rbrack} = {{{\overset{\sim}{S}}_{k}^{H}\left( {{H^{H}H} + {\frac{\sigma^{2}}{ɛ}I}} \right)}^{- 1}{\overset{\sim}{S}}_{k}}},$

[0076] and for zero-forcing chip equalization, the$\frac{\sigma^{2}}{ɛ}$

[0077] I term vanishes. E[{circumflex over (n)}{circumflex over(n)}^(H)] is an NP x NP matrix, and E[{circumflex over(n)}(i){circumflex over (n)}(i)^(H)] represents the N blocks ofdimension P x P on the diagonal of E[{circumflex over (n)}{circumflexover (n)}^(H)]. The spatial channel matrix G_(C)(i) is produced by G_(C)generator 129.

[0078] Successive spatial interference cancellation (zero forcing orMMSE) is then applied at 85 to the KN vectors of dimension P×1 producedby the preconditioner 123.

[0079] Considering now exemplary multi-user detection embodiments of theinvention (shown in FIG. 13), recall from equation (6) that y=ab+n, so

{circumflex over (b)}=F _(M) y=F _(M) ab+F _(M) n, where F _(M) =F _(MZ)or F _(MM).

[0080] Similar to the chip-level equalizer, the embodiments of FIG. 13isolate square blocks of size P×P on the diagonal of F_(M)a:

F _(M) y=Rb+(F _(M) a−R)b+F _(M) n  (30)

[0081] where F_(M)y produced by multi-user detector 130 (also referredto herein as a linear front end detector) is a KNP×1 vector, and R issimilar to B above, but the diagonal of R is composed of KN blocks ofdimension P×P on the diagonal of FM a.

[0082] Each block is now isolated, which corresponds to one space-symbol(i.e., P symbols over P antennas) of a single source,

[F _(M) y] _(k,i) =R _(i) b _(k,i) +{circumflex over (n)} _(k,i) i=1, .. . , N and k=1, . . . K

[0083] where [F_(M)y]_(k,i) is a P×1 vector. The isolation operationperformed on F_(M)y by separator 131 is illustrated in FIG. 14.

[0084] Also, E[{circumflex over (n)}{circumflex over (n)}^(H)]=C_(i) canbe readily calculated from equation (30) analogously to the calculationof C_(i) demonstrated above relative to equation (28), namely as a P×Pblock on the diagonal of (F_(M)−R) (F_(M)a−R)^(H)+F_(M)F_(M) ^(H).

[0085] Also, E[b_(i){circumflex over (n)}_(i) ^(H)]=O, because theblocks on the diagonal of (F_(M)a−R) are 0, and E[b_(i)b_(i) ^(H)]=ε.

[0086] Successive spatial interference cancellation can be performedwith respect to each P×1 vector [F_(M)y]_(k,i) produced by separator131.

[0087] In other exemplary multi-user detection embodiments (shown inFIG. 15), the expression b=F_(M)ab+F_(M)n can be written as

{circumflex over (b)}=b+(F _(M) a−I)b+F _(M) n

Let {circumflex over (n)}=(F _(M) a−I)b+F _(M)n

[0088] Isolating a single source k, and a single time instance i, take Psymbols of {circumflex over (b)} (here this is done for k=1, . . . , Kand i=1, . . . ,N),and label as {circumflex over (b)}_(k,i). Hence{circumflex over (b)}, a KNP×1 vector, is separated into KN vectors ofdimension P×1, namely {circumflex over (b)}_(k,i)=b_(k,i)+{circumflexover (n)}k,i. This separation operation, performed by separator 152, isshown in FIG. 16.

[0089] A preconditioner 153 preconditions the KN vectors {circumflexover (b)}_(k,i) (i.e., reintroduces the spatial channel) with acorresponding matrix G_(M)(k,i), so that the residual interference{circumflex over (n)} is uncorrelated, i.e.

G _(M)(k,i)=(E[{circumflex over (n)} _(k,i) {circumflex over (n)} _(k,i)^(H)])^(−1/2)

G _(M)(k,i){circumflex over (b)} _(k,i) =G _(M)(k,i){circumflex over(b)} _(k,i) +G _(M)(k,i){circumflex over (n)} _(k,i)

[0090] For MMSE multi-user detection,${{E\left\lbrack {\hat{\underset{\_}{n}}{\hat{\underset{\_}{n}}}^{H}} \right\rbrack} = \left( {{a^{H}a} + {\frac{\sigma^{2}}{ɛ}I}} \right)^{- 1}},$

[0091] and for zero-forcing multi-user detection, the$\frac{\sigma^{2}}{ɛ}$

[0092] I term vanishes. For multi-user detection, E[{circumflex over(n)}{circumflex over (n)}^(H)] is a KNP×KNP matrix, and E[{circumflexover (n)}_(k,i){circumflex over (n)}_(k,i)] represents the KN blocks ofdimension P×P on the diagonal of E[{circumflex over (n)}{circumflex over(n)}^(H)]. The spatial channel matrix G_(M)(k,n) is produced by G_(M)generator 159.

[0093] Successive spatial interference cancellation is performed at 85on the KN vectors of dimension P×1 produced by the preconditioner 153.For successive spatial interference cancellation, assume a model:

w=Tv+n} where v is P×1, w is P×1 and T is P×P

[0094] a) for conventional zero forcing (ZF) spatial interferencecancellation:

[0095] for j=1:P

[0096] L=(T^(H)T)⁻¹T^(H)w

[0097] {circumflex over (v)}(j)=hard decision (L(1));

[0098] update T (essentially cross out first column of T)

[0099] w=w−{circumflex over (v)}(j)×[1^(st) column of old T]

[0100] end

[0101] b) for conventional MMSE spatial interference cancellation:

[0102] If the noise is not white, i.e., if C≠σ²I, (whereC=D_(i)C_(i)D_(i) ^(H) for chip equalization embodiments and C=C_(i) formulti-user detection embodiments), whiten the noise first:

ŵ=C ^(−1/2) w=C ^(−1/2) Tv+C ^(−1/2) n, where

[0103] C^(−1/2)T={circumflex over (T)}, and C^(−1/2)n={circumflex over(n)} (which is white). So, ŵ={circumflex over (T)}v+{circumflex over(n)}. The procedure for MMSE successive spatial interferencecancellation is then the same as for ZF above, but with w replaced by ŵ,T replaced by {circumflex over (T)} and (T^(H)T)⁻¹ replaced by({circumflex over (T)}^(H){circumflex over (T)}+I)⁻¹.

[0104] If the noise is white, then MMSE successive spatial interferencecancellation differs from ZF successive spatial interferencecancellation only by replacing (T^(H)T)⁻¹ with (T^(H)T+I)⁻¹.

[0105] The Mean Squared Error (MSE) for each symbol is computed on thediagonal of ({circumflex over (T)}^(H){circumflex over (T)}+I)⁻¹ (or thediagonal of (T^(H)T+I)⁻¹), and the algorithm can be further improved, insome embodiments, by detecting the P symbols in order of increasing MSE,instead of in the order of j=1, . . . P shown above.

[0106]FIG. 17 diagrammatically illustrates pertinent portions ofexemplary embodiments of the successive interference cancellationapparatus 85 of FIGS. 8, 10, 12, 13 and 15. This apparatus is forprocessing the KN vectors of dimension P×1 produced by the embodimentsof FIGS. 8, 10, 12, 13 and 15. The interference cancellation apparatusof FIG. 17 includes KN successive interference cancellers, one for eachof the received P×1 vectors. Each canceller receives its associatedvector at the w input thereof, and each canceller produces its symboldecisions at the v output thereof. Each canceller can perform theexemplary successive interference cancellation operations describedabove, either zero-forcing or MMSE, to produce the symbol decisions atthe v output in response to the vector received at the w input. Each ofthe cancellers also receives from a controller 161 appropriate controlinputs 166 for use in conjunction with the input vector to produce thesymbol decisions. Advantageously, the matrix T is smaller than thematrices F_(CZ), F_(CM), F_(MZ) and F_(MM), which simplifies the matrixcomputations of the successive interference cancellation, as compared toconventional approaches. Further advantageously, the successiveinterference cancellation apparatus of FIG. 17 can process each of theKN vectors simultaneously.

[0107]FIG. 18 illustrates in tabular format examples of controlinformation which can be provided at 171 to the controller 161 (see alsoFIG. 17) of the interference cancellation apparatus 85 in the variousembodiments of FIGS. 8, 10, 12, 13 and 15. FIG. 18 also illustratesinformation produced by the controller 161 in response to the receivedcontrol information. The matrix T in column 171 is provided bycontroller 161 as control input to each of the interference cancellersin zero-forcing interference canceller embodiments, and in MMSEinterference canceller embodiments where the noise is white. The matrixC in column 172 is not provided as control input to the interferencecancellers, but is used (together with T) by controller 161 in MMSEinterference canceller embodiments to produce the information in columns173 and 174. The information in columns 173 ({circumflex over (T)}) and174 (({circumflex over (T)}^(H){circumflex over (T)}+I)⁻¹) is providedby controller 161 as control input to each of the interferencecancellers in MMSE embodiments if the noise is not white, and theinformation in column 175 ((T^(H)T+I)⁻¹) is provided by controller 161as control input to each of the interference cancellers in MMSEembodiments if the noise is white.

[0108] Referring again to the example of FIG. 17, the symbol decisionsproduced by the successive interference cancellation apparatus areprovided to a data extraction apparatus which extracts the communicationdata from the symbol decisions. This data extraction apparatus includesa demodulation section, which is followed in turn by a channelde-interleaver section, and a channel decoding section. A conventionaldata processing section is coupled to the channel decoding section. Thedata processing section can be implemented, for example, with amicroprocessor or digital signal processor, for performing desired dataprocessing operations on the data provided by the channel decodingsection.

[0109]FIG. 19 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a wireless CDMA receiver according to theinvention. FIG. 19 illustrates that the KN vectors of dimension P×1produced by the embodiments of FIGS. 8, 10, 12, 13 and 15 can be inputto respective ones of KN conventional maximum likelihood detectors. Insuch embodiments, the desired interference rejection operation isperformed by the maximum likelihood detectors instead of by thesuccessive interference cancellers of FIG. 17.

[0110]FIG. 20 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a wireless CDMA receiver according to theinvention. FIG. 20 illustrates that interference rejection (e.g.,successive interference cancellation or maximum likelihood detection)can be applied to vectors of dimension N×1 and NP×1, in addition to theP×1 vectors described above with respect to the aforementionedembodiments. In particular, the separators of the aforementionedembodiments of FIGS. 8, 10, 12, 13 and 15 could perform aseparation/isolation operation that causes KP vectors of dimension N×1to be presented to the interference rejection unit, or could perform aseparation/isolation operation that causes K vectors of dimension NP×1to be presented to the interference rejection unit. The KP vectors ofdimension N×1 each correspond to a given user and a given transmitantenna during each of N symbol transmit times, and the K vectors ofdimension NP×1 each correspond to a given user during a selected numberof symbol transmit times on a selected number of transmit antennas,wherein NP is the product of the selected number of transmit times andthe selected number of transmit antennas.

[0111] Although the exemplary embodiments illustrated in FIGS. 8-20assume for clarity of exposition that all of the K information sourcesof FIG. 2 are of interest to the user equipment represented by theembodiments of FIGS. 8-18, other exemplary embodiments where less thanall K sources are of interest to the user equipment are readily andeasily implemented by suitable scaling to produce K₁N vectors ofdimension P×1 at the input of interference cancellation apparatus 85,where K₁ is less than K.

[0112] It will be evident to workers in the art that the communicationreceiver embodiments of FIGS. 8-20 can be readily implemented, forexample, by suitably modifying software, or a combination of softwareand hardware, in conventional wireless communication receivers such asCDMA receivers. Some specific examples of such communication receiversare fixed site wireless communication base stations and mobile wirelesscommunication stations.

[0113] Although exemplary embodiments of the invention are describedabove in detail, this does not limit the scope of the invention, whichcan be practiced in a variety of embodiments.

What is claimed is:
 1. An apparatus for processing a received wirelesscommunication signal, comprising: an input for receiving a sample vectorwhich includes a plurality of sample values and which represents atimewise corresponding wireless communication signal portion receivedvia a plurality of receive antennas and produced by a transmitter inwhich each of a plurality of information sources transmits a pluralityof symbols via respective ones of a plurality of transmit antennasduring each of a plurality of transmit time intervals associated withsaid wireless communication signal portion; an input processing sectioncoupled to said input for producing from the sample vector a pluralityof vectors that are smaller than the sample vector; and an interferencerejection unit coupled to said input processing section for applying aninterference rejection operation to each of said smaller vectorsindividually to thereby decide said symbols.
 2. The apparatus of claim1, wherein said input processing section includes a chip equalizercoupled to said input for applying a chip equalization operation to saidsample vector to thereby produce a chip equalization result vector. 3.The apparatus of claim 2, wherein said input processing section includesa separator coupled to said chip equalizer for separating said chipequalization result vector into a plurality of intermediate vectors. 4.The apparatus of claim 3, wherein said input processing section includesa despreader coupled between said interference rejection unit and saidseparator for applying a plurality of spreading codes to saidintermediate vectors to effectuate a despreading operation that producessaid smaller vectors.
 5. The apparatus of claim 4, wherein saidintermediate vectors respectively correspond to said transmit timeintervals, and wherein each of said smaller vectors corresponds to arespective one of said information sources during a respective one ofsaid transmit time intervals.
 6. The apparatus of claim 3, wherein saidintermediate vectors respectively correspond to said transmit timeintervals.
 7. The apparatus of claim 2, wherein said chip equalizationoperation includes one of a zero-forcing chip equalization operation anda minimum mean squared error chip equalization operation.
 8. Theapparatus of claim 7, wherein said interference rejection operationincludes one of a successive interference cancellation operation and amaximum likelihood detection operation.
 9. The apparatus of claim 8,wherein said successive interference cancellation operation includes oneof a zero-forcing successive interference cancellation operation and aminimum mean squared error successive interference cancellationoperation.
 10. The apparatus of claim 2, wherein said input processingsection includes a despreader coupled to said chip equalizer forapplying a plurality of spreading codes to said chip equalization resultvector to effectuate a despreading operation that produces anintermediate vector.
 11. The apparatus of claim 10, wherein said inputprocessing section includes a separator coupled to said despreader forseparating said intermediate vector into a plurality of further vectors.12. The apparatus of claim 11, wherein each said further vectorcorresponds to a respective one of said information sources during arespective one of said transmit time intervals.
 13. The apparatus ofclaim 11, wherein said further vectors are said smaller vectors.
 14. Theapparatus of claim 11, wherein said input processing section includes apreconditioner coupled between said separator and said interferencerejection unit for processing said further vectors to whiten respectivenoise components thereof and thereby produce a corresponding pluralityof preconditioned vectors whose respective noise components are white.15. The apparatus of claim 14, wherein said preconditioned vectors aresaid smaller vectors.
 16. The apparatus of claim 1, wherein saidinterference rejection operation includes one of a successiveinterference cancellation operation and a maximum likelihood detectionoperation.
 17. The apparatus of claim 16, wherein said successiveinterference cancellation operation includes one of a zero-forcingsuccessive interference cancellation operation and a minimum meansquared error successive interference cancellation operation.
 18. Theapparatus of claim 1, wherein said input processing section includes amulti-user detector coupled to said input for applying a multi-userdetection operation to said sample vector to produce a multi-userdetection result vector.
 19. The apparatus of claim 18, wherein saidinput processing section includes a separator coupled to said multi-userdetector for separating said multi-user detection result vector into aplurality of further vectors.
 20. The apparatus of claim 19, whereineach said further vector corresponds to a respective one of saidinformation sources during a respective one of said transmit timeintervals.
 21. The apparatus of claim 19, wherein said further vectorsare said smaller vectors.
 22. The apparatus of claim 19, wherein saidinput processing section includes a preconditioner coupled between saidseparator and said interference rejection unit for processing saidfurther vectors to whiten respective noise components thereof andthereby produce a corresponding plurality of preconditioned vectorswhose respective noise components are white.
 23. The apparatus of claim22, wherein said preconditioned vectors are said smaller vectors. 24.The apparatus of claim 18, wherein said multi-user detection operationis one of a zero-forcing multi-user detection operation and a minimummean squared error multi-user detection operation.
 25. The apparatus ofclaim 24, wherein said interference rejection operation includes one ofa successive interference cancellation operation and a maximumlikelihood detection operation.
 26. The apparatus of claim 25, whereinsaid successive interference cancellation operation is one of azero-forcing successive interference cancellation operation and aminimum mean squared error successive interference cancellationoperation.
 27. The apparatus of claim 1, wherein said interferencerejection unit is for applying said interference rejection operation toeach of said smaller vectors simultaneously.
 28. A wirelesscommunication receiving apparatus, comprising: a plurality of receiveantennas for receiving a wireless communication signal; a samplercoupled to said receive antennas for producing a sample vector whichincludes a plurality of sample values and which represents a timewisecorresponding portion of said wireless communication signal, saidwireless communication signal portion produced by a transmitter in whicheach of a plurality of information sources transmits a plurality ofsymbols via respective ones of a plurality of transmit antennas duringeach of a plurality of transmit time intervals associated with saidwireless communication signal portion; an input processing sectioncoupled to said sampler for producing from said sample vector aplurality of vectors that are smaller than said sample vector; aninterference rejection unit coupled to said input processing section forapplying an interference rejection operation to each of said smallervectors individually to thereby decide said symbols; a data extractorcoupled to said interference rejection unit for extracting communicationdata from the symbols decided by said interference rejection unit; and adata processing apparatus coupled to said data extractor for performingdata processing operations on said extracted data.
 29. The apparatus ofclaim 28, provided as a CDMA receiver.
 30. The apparatus of claim 28,wherein said input processing section includes a chip equalizer coupledto said input for applying a chip equalization operation to said samplevector to thereby produce a chip equalization result vector.
 31. Theapparatus of claim 30, wherein said input processing section includes aseparator coupled to said chip equalizer for separating said chipequalization result vector into a plurality of intermediate vectors. 32.The apparatus of claim 31, wherein said input processing sectionincludes a despreader coupled between said interference rejection unitand said separator for applying a plurality of spreading codes to saidintermediate vectors to effectuate a despreading operation that producessaid smaller vectors.
 33. The apparatus of claim 32, wherein saidintermediate vectors respectively correspond to said transmit timeintervals, and wherein each of said smaller vectors corresponds to arespective one of said information sources during a respective one ofsaid transmit time intervals.
 34. The apparatus of claim 31, whereinsaid intermediate vectors respectively correspond to said transmit timeintervals.
 35. The apparatus of claim 30, wherein said input processingsection includes a despreader coupled to said chip equalizer forapplying a plurality of spreading codes to said chip equalization resultvector to effectuate a despreading operation that produces anintermediate vector.
 36. The apparatus of claim 35, wherein said inputprocessing section includes a separator coupled to said despreader forseparating said intermediate vector into a plurality of further vectors.37. The apparatus of claim 36, wherein each said further vectorcorresponds to a respective one of said information sources during arespective one of said transmit time intervals.
 38. The apparatus ofclaim 36, wherein said further vectors are said smaller vectors.
 39. Theapparatus of claim 36, wherein said input processing section includes apreconditioner coupled between said separator and said interferencerejection unit for processing said further vectors to whiten respectivenoise components thereof and thereby produce a corresponding pluralityof preconditioned vectors whose respective noise components are white.40. The apparatus of claim 39, wherein said preconditioned vectors aresaid smaller vectors.
 41. The apparatus of claim 28, wherein said inputprocessing section includes a multi-user detector coupled to said inputfor applying a multi-user detection operation to said sample vector toproduce a multi-user detection result vector.
 42. The apparatus of claim41, wherein said input processing section includes a separator coupledto said multi-user detector for separating said multi-user detectionresult vector into a plurality of further vectors.
 43. The apparatus ofclaim 42, wherein each said further vector corresponds to a respectiveone of said information sources during a respective one of said transmittime intervals.
 44. The apparatus of claim 42, wherein said furthervectors are said smaller vectors.
 45. The apparatus of claim 42, whereinsaid input processing section includes a preconditioner coupled betweensaid separator and said interference rejection unit for processing saidfurther vectors to whiten respective noise components thereof andthereby produce a corresponding plurality of preconditioned vectorswhose respective noise components are white.
 46. The apparatus of claim45, wherein said preconditioned vectors are said smaller vectors. 47.The apparatus of claim 28, wherein said interference rejection unit isfor applying said interference rejection operation to each of saidsmaller vectors simultaneously.
 48. A method of processing a receivedwireless communication signal, comprising: receiving a wirelesscommunication signal via a plurality of receive antennas; producing asample vector which includes a plurality of sample values and whichrepresents a timewise corresponding portion of said wirelesscommunication signal, said wireless communication signal portionproduced by a transmitter in which each of a plurality of informationsources transmits a plurality of symbols via respective ones of aplurality of transmit antennas during each of a plurality of transmittime intervals associated with said wireless communication signalportion; producing from said sample vector a plurality of vectors thatare smaller than said sample vector; and applying an interferencerejection operation to each of said smaller vectors individually tothereby decide said symbols.
 49. The method of claim 48, wherein saidlast-mentioned producing step includes applying a chip equalizationoperation to said sample vector to thereby produce a chip equalizationresult vector.
 50. The apparatus of claim 49, wherein saidlast-mentioned producing step includes separating said chip equalizationresult vector into a plurality of intermediate vectors.
 51. Theapparatus of claim 50, wherein said last-mentioned producing stepincludes applying a plurality of spreading codes to said intermediatevectors to effectuate a despreading operation that produces said smallervectors.
 52. The apparatus of claim 51, wherein said intermediatevectors respectively correspond to said transmit time intervals, andwherein each of said smaller vectors corresponds to a respective one ofsaid information sources during a respective one of said transmit timeintervals.
 53. The method of claim 50, wherein said intermediate vectorsrespectively correspond to said transmit time intervals.
 54. The methodof claim 49, wherein said last-mentioned producing step includesapplying a plurality of spreading codes to said chip equalization resultvector to effectuate a despreading operation that produces anintermediate vector.
 55. The method of claim 54, wherein saidlast-mentioned producing step includes separating said intermediatevector into a plurality of further vectors.
 56. The method of claim 55,wherein each said further vector corresponds to a respective one of saidinformation sources during a respective one of said transmit timeintervals.
 57. The method of claim 55, wherein said further vectors aresaid smaller vectors.
 58. The method of claim 55, wherein saidlast-mentioned producing step includes preconditioning said furthervectors, including processing said further vectors to whiten respectivenoise components thereof and thereby produce a corresponding pluralityof preconditioned vectors whose respective noise components are white.59. The method of claim 58, wherein said preconditioned vectors are saidsmaller vectors.
 60. The method of claim 48, wherein said last-mentionedproducing step includes applying a multi-user detection operation tosaid sample vector to produce a multi-user detection result vector. 61.The method of claim 60, wherein said last-mentioned producing stepincludes separating said multi-user detection result vector into aplurality of further vectors.
 62. The method of claim 61, wherein eachsaid further vector corresponds to a respective one of said informationsources during a respective one of said transmit time intervals.
 63. Themethod of claim 61, wherein said further vectors are said smallervectors.
 64. The method of claim 61, wherein said last-mentionedproducing step includes preconditioning said further vectors, includingprocessing said further vectors to whiten respective noise componentsthereof and thereby produce a corresponding plurality of preconditionedvectors whose respective noise components are white.
 65. The method ofclaim 64, where said preconditioned vectors are said smaller vectors.66. The method of claim 48, wherein said applying step includes applyingsaid interference rejection operation to each of said smaller vectorssimultaneously.
 67. The method of claim 48, wherein said interferencerejection operation includes one of a successive interferencecancellation operation and a maximum likelihood detection operation. 68.A wireless communication receiver apparatus, comprising: a receiveantenna apparatus for receiving a wireless communication signal; asampler coupled to said receive antenna apparatus for producing a samplevector which includes a plurality of sample values and which representsa timewise corresponding portion of said wireless communication signal;a linear front end detector coupled to said sampler for applying adetection operation to said sample vector to produce a detection resultvector; an interference rejection unit coupled to said linear front enddetector for applying an interference rejection operation to informationfrom said detection result vector to make decisions regarding symbolscarried by said wireless communication signal portion; a data extractorcoupled to said interference rejection unit for extracting communicationdata from the symbols decided by said interference rejection unit; and adata processing apparatus coupled to said data extractor for performingdata processing operations on said extracted data.
 69. The apparatus ofclaim 68, wherein said linear front end detector includes a chipequalizer and said detection operation includes a chip equalizationoperation.
 70. The apparatus of claim 69, wherein said chip equalizationoperation is one of a zero-forcing chip equalization operation and aminimum mean squared error chip equalization operation.
 71. Theapparatus of claim 68, wherein said linear front end detector includes amulti-user detector, and said detection operation includes a multi-userdetection operation.
 72. The apparatus of claim 71, wherein saidmulti-user detection operation is one of a zero-forcing multi-userdetection operation and a minimum mean squared error multi-userdetection operation.
 73. The apparatus of claim 68, provided as a CDMAreceiver.
 74. The apparatus of claim 68, wherein said interferencerejection operation is one of a successive interference cancellationoperation and a maximum likelihood detection operation.
 75. Theapparatus of claim 74, wherein said successive interference cancellationoperation is one of a zero-forcing successive interference cancellationoperation and a minimum mean squared error successive interferencecancellation operation.
 76. The apparatus of claim 68, including aseparating portion coupled to said linear front end detector forproducing from said detection result vector a plurality of vectors thatare smaller than said detection result vector, said interferencerejection unit for applying said interference rejection operation toeach of said smaller vectors individually.
 77. The apparatus of claim76, wherein said interference rejection unit is for applying saidinterference rejection operation to each of said smaller vectorssimultaneously.
 78. The apparatus of claim 76, wherein said separatingportion includes a despreader.
 79. An apparatus for processing areceived wireless communication signal, comprising: an input forreceiving a sample vector which includes a plurality of sample valuesand which represents a timewise corresponding portion of a wirelesscommunication signal received via a receive antenna apparatus; a linearfront end detector coupled to said input for applying a detectionoperation to said sample vector to produce a detection result vector;and an interference rejection unit coupled to said linear front enddetector for applying an interference rejection operation to saiddetection result vector to make decisions regarding symbols carried bysaid wireless communication signal portion.
 80. The apparatus of claim79, wherein said linear front end detector includes a chip equalizer andsaid detection operation includes a chip equalization operation.
 81. Theapparatus of claim 80, wherein said chip equalization operation is oneof a zero-forcing chip equalization operation and a minimum mean squarederror chip equalization operation.
 82. The apparatus of claim 79,wherein said linear front end detector includes a multi-user detector,and said detection operation includes a multi-user detection operation.83. The apparatus of claim 82, wherein said multi-user detectionoperation is one of a zero-forcing multi-user detection operation and aminimum mean squared error multi-user detection operation.
 84. Theapparatus of claim 79, wherein said interference rejection operation isone of a successive interference cancellation operation and a maximumlikelihood detection operation.
 85. The apparatus of claim 84, whereinsaid successive interference cancellation operation is one of azero-forcing successive interference cancellation operation and aminimum mean squared error successive interference cancellationoperation.
 86. The apparatus of claim 79, including a separating portioncoupled to said linear front end detector for producing from saiddetection result vector a plurality of vectors that are smaller thansaid detection result vector, said interference rejection unit forapplying said interference rejection operation to each of said smallervectors individually.
 87. The apparatus of claim 86, wherein saidinterference rejection unit is for applying said interference rejectionoperation to each of said smaller vectors simultaneously.
 88. Theapparatus of claim 86, wherein said separating portion includes adespreader.